1. Field of the Invention
The present invention relates to a battery state monitoring circuit for detecting a voltage and an abnormality of a secondary battery, and to a battery device. More particularly, the present invention relates to a battery state monitoring circuit having a function of predicting a state of charge of the secondary battery and a function of evaluating deterioration of the secondary battery, and to a battery device.
2. Description of the Related Art
FIG. 5 is a schematic diagram for illustrating a related-art battery device including a battery state monitoring circuit. The related-art battery device includes a battery state monitoring circuit, a secondary battery 501, a current source 511, a current source 512, and a switching circuit 510. The secondary battery 501 can be represented by an equivalent circuit of a battery capacitor 502, a resistor 503, a resistor 504, and a capacitor 505. The switching circuit 510 is operated to switch the current source 511 and the current source 512. The current source 511 and the current source 512 cause currents having different current values I1 and I2, respectively, to flow.
The switching circuit 510 switches the current source 511 and the current source 512 so that a charge current to the secondary battery 501 is periodically changed. Then, a voltage of the secondary battery is measured at the respective time points, to thereby determine resistance values of the resistor 503 and the resistor 504.
A method of evaluating a lifetime of the secondary battery with the use of those resistance values is disclosed (for example, see Japanese Patent Application Laid-open No. 2000-133322).